NEW YORK— Dubai-based Istithmar, suddenly a force in luxury hotel real estate, has acquired a 73% interest in the 248-room Mandarin Oriental New York, paying approximately $1.37 million a key. The per key figure is based on a total property valuation of $340 million, he number provided by Mandarin Oriental. Late last year, Istithmar also acquired the W Hotel Union Square in New York, paying slightly over $1 million a key. The sellers were Apollo Real Estate and Mandarin Oriental itself. Mandarin remains a significant minority owner and will retain management of the luxury property. The Mandarin Oriental has become a centerpiece of the high-profile Time Warner Center at Columbus Circle on Manhattans West Side.